1. Field of the Invention
The present invention relates generally to a drilling machine, and more particularly to a drilling machine which has a number of tools therein. Said drilling machine automatically selects a desired tool and functions like a so-called drilling machine with an automatic tool changer (A.T.C.).
2. Description of the Prior Art
A drilling machine with an automatic tool changer is basically comprised of: a table which is slidably located on a bed and moves a workpiece to any desired position in a horizontal plane; a tool for machining said workpiece; a spindle, to which said tool is detachably connected, which rotates together with said tool; a spindle head by which said spindle is rotatably held; a spindle driving motor for rotating said spindle; a lead or feed screw for moving said spindle head up and down, and; a driving motor for rotating said lead screw. In the above described drilling machine with an automatic tool changer, said tool is one of a predetermined number of tools. These tools are rotatably held by a circular tool magazine and are arranged at a constant pitch along the periphery thereof. Furthermore, said circular tool magazine is rotatable with respect to the spindle head in an intermittent motion. Each of the tools comes under the spindle when the circular tool magazine rotates in an intermittent motion. When one of the tools is needed for a machining operation, for example, drilling, the spindle head is traversed upward by the driving motor, together with the spindle and also with the spindle driving motor, by means of the lead screw. Then, the tool magazine can freely rotate without running against the spindle. Subsequently, the desired tool comes under the spindle and the axis of the desired tool is aligned with the axis of the spindle. After this, the spindle head is traversed downward, thereby connecting the spindle with the desired tool.
In a drilling machine with an automatic tool changer according to the prior art, non-working tools, in particular non-working tools adjacent to a working tool may interfere with a workpiece during a machining operation since the non-working tools protrude outwardly and downwardly. That is, when the working tool is moving downward together with the tool magazine to machine a workpiece, for example, to drill a workpiece, the non-working tools adjacent to the working tool come into contact with the workpiece and obstruct the machining work. Furthermore, a similar problem occurs in the case of different kinds of tools arranged in the tool magazine. That is, for example in the case of a working tool being shorter than the non-working tools adjacent to it, there is the possibility that the non-working tools will come into contact with the workpiece prior to the working tool and obstruct the contact of the working tool with the workpiece, so that the desired machining becomes impossible to carry out. To solve this problem, it is necessary to enlarge the circular tool magazine, i.e. to increase the radius of the circular tool magazine in which a plurality of tools are arranged at a constant pitch along the periphery thereof, resulting in a large sized apparatus.